Trouble changing primitive attributes
Adding a response, because I came here looking for an answer.

Blender 2.80 (beta), as of 2019-feb-02 nightly build:

The parameters for a newly added primitive are not in the T-side-panel (as previously in Blender 2.79). 

Instead they have a pop-up panel in lower-left corner overlaying the 3D-View. 

When you first start running Blender-2.80, this pop-up may be minimized (as shown in the first image). Click this to open this panel. It may remain automatically opened for newly added primitives after you open it the first time.